This invention relates to switches such as limit switches and key switches usable for doors that are electromagnetically locked.
A key switch is often used on a door to a work area with power machine tools for switching power on and off by detecting the opening and closing of the door. A key is usually operated on the door while the main part of the door switch is set on a fixed frame at the doorway such that the power source for the machine tools is switched on when the door is closed and the key is inserted into a keyhole provided to the main part of the switch and switched off when the door is opened and the key is pulled out from the main part.
FIG. 15A and FIG. 15B show such a key switch with a main case 71 containing a plunger 70 which is upwardly biased by way of a spring (not shown) and a head case 73 provided with a key hole 74, and a rotary cam 72 contacting the upper end of the plunger 70 connected to the main case 71. As the cam is rotated to displace the plunger 70, a mobile terminal (not shown) associated with the plunger 70 contacts or moves away from a fixed terminal, thereby switching on and off the switch mechanism. FIG. 15A shows a key 75 not yet inserted into the keyhole 74 and the plunger 70 remaining in the pushed-in condition against the biasing force thereon such that the switch is in the switched-off condition. When the key 75 is inserted into the keyhole 74 and the door is closed, the cam 72 has rotated and the plunger 70 is released from the pushed-in condition, thereby allowing the mobile terminal to contact the fixed terminal to bring the switch into the switched-on condition.
A key switch thus structured remains in the switched-off condition unless the key 75 is inserted because the cam 72 inside the head case 73 keeps the plunger 70 pushed in. If the head case 73 is removed for a maintenance work or happens to be knocked away accidentally from the main case 71 by an external force, the force pushing in the plunger 70 may be diminished, allowing the plunger 70 to be moved by the biasing force thereon and to bring about the switched-on condition.
Thus, at the time of a maintenance work when the head case 73 is removed from the main case 71, say, for replacing a damaged head case with a new one or changing the direction of insertion of the key, the machine tools under the control of the switch may be inadvertently switched on. A similar situation may come about when wires are being connected to the main case 71 while the head case 73 is disconnected from the main case 71. Thus, it has been a common practice to switch off a source switch situated somewhere else before such work is carried out and to switch on the source switch after the work has been completed.
If an excessive force is applied to the head case 73 as the door is opened or closed and the head case 73 becomes removed from the main case 71, the door may open while the machine tools remain switched on. This may happen, for example, when the door is not provided with a door stopper and is closed with a bang such that the impulsive force of the closing is directly communicated to the head case 73. If the door is sufficiently heavy, the impulse may be sufficiently large to displace the head case 73. Moreover, when the door is closed while the key is deformed, the key 75 may hit the head case 73 without being inserted into the keyhole 74, causing the head case 73 to fly off the main case 71.
In the case of a key switch with an electromagnetic interlocking mechanism, adapted to lock its switching mechanism when the door is closed, if the electromagnetic lock is used as a lock for the door without using a hook or a latch, the head case 73 may become removed from the main case 71 when the door is forcibly opened without releasing the electromagnetic lock because the cam inside the main body is not allowed to rotate by the switching mechanism and the key is being forcibly pulled with the door while being hooked to the cam.
There are two kinds door switches for electromagnetically locking. With the mechanical lock type, the door becomes automatically locked when it is closed by a locking mechanism by a biasing force and the door is released from the locked condition by passing a current through a solenoid. With the solenoid lock type, the door is not immediately locked when it is closed and its locked condition continues only while a current passes through a solenoid to overcome the biasing force which keeps the locking mechanism in an open condition, the opening of the door becoming allowed by stopping the current through the solenoid.
With either kind, if the door is forcibly opened without carrying out the proper unlocking process while the door remains locked, the cam inside is forcibly rotated with the key pulled. As a result, the cam or the plunger operated thereby may be damaged and the cam may rotate to open the door. Thus, the power circuit may remain switched on although the door is open, the machine tools in the work area being kept running.
It is therefore an object of this invention to provide a switch capable of operating correctly even if the head case is inadvertently removed from the main body without causing the switching mechanism to operate erratically.
It is another object of this invention to provide a switch capable of operating correctly even if the key is forcibly pulled out while the switch is locked.
In one aspect, the invention relates to a switch characterized as comprising a main case including a switching mechanism and a forcing means and a head case containing an operating mechanism for the switching mechanism, wherein the head case is normally attached to the main case, the switching mechanism is subjected to a biasing force, the switching mechanism and the operating mechanism are correlated such that the switching means is kept in a first switched condition (or the switched-off condition) by opposing against the biasing force when no external operation is being effected on the operating mechanism, the switching mechanism is displaced by the biasing force and is set in a second switched condition (or the switched-on condition) when an external operation is effected on the operating mechanism, the forcing means serves to set the switching mechanism in the first switched condition by a forced displacement operation on the switching mechanism, the forcing means is released from the forced displacement operation when the head case is properly connected to the main case, and the forcing means carries out the forced displacement operation when the head case is not properly connected to the main case.
In the above, xe2x80x9cno external operation being effected on the operating mechanismxe2x80x9d means that nothing is being done to operate the switch, for example, by inserting a key if the switch is a key switch. The condition that the head case and the main case are not properly connected may occur when at least a portion of the head case is separated from the main case. Thus, according to this aspect of the invention, the forcing means does not operate when the head case and the main case are normally attached but when they become separated either intentionally or accidentally, this function is activated and the switching mechanism is forcibly maintained in the first switched condition in spite of the biasing force thereon to switch it to the second switched condition.
According to a preferred embodiment of the invention, the aforementioned switching mechanism includes fixed terminals, mobile terminals, a mobile member supporting these mobile terminals and a returning spring applying a force on the mobile member so as to bring about the second switched condition (or the switched-on condition) where the mobile terminals contact the fixed terminals. The first switched condition (or the switched-off condition) is where the fixed terminals and the mobile terminals are separated and is realized by displacing the mobile member against the biasing force of the returning spring. The operating mechanism comprises a plunger which contacts the mobile member, and the forcing means serves to forcibly displace the plunger. The plunger and the mobile member may be formed integrally or may be separable components. If the switch is so structured that power is supplied to machine tools, for example, when the switch is in the second switched condition, the forcing means of this invention can prevent waste of power when the head case becomes inadvertently separated from the main case.
The forcing means may be formed with a forcing member for forcing the plunger and a biasing member for biasing this forcing member towards the plunger, the forcing member being retracted against the forcing member to a retracted position not preventing the plunger from being displaced when the head case is normally connected to the main case, and the biasing member causing the forcing member to forcibly displace the plunger against the returning spring when the head case is separated from the main case. Such a forcing member may be adapted to undergo a reciprocating (swinging) motion or a rotary motion to push the plunger into undergoing a forcible displacement, depending on the kind of biasing force on the switching mechanism and the condition of stroking.
According to another embodiment of the invention, the forcing member comprises a spring member having an operating part which exerts a force on the plunger and being adapted to be elastically deformed by contacting a portion of the head case connected to the main case such that the operating part is moved to a retracted position not interfering with the displacement of the plunger. The operating part serves to cause the plunger to be forcibly displaced against the force of the returning spring when the spring member becomes separated from the portion of the head case. By using such a spring member as the forcing means of this invention, it becomes unnecessary to provide a dedicated force-providing means and hence the structure of the switch can be made simpler and the production cost can be reduced. The spring member may be provided with a lever contacting a portion of the head case such that the elastic deformation of the spring member can be controlled by the lever ratio so as to retract the operating part to a specified retracted position. By using such a lever, even a strong spring member can be easily deformed. The spring member may preferably be formed by a plate spring with the operating part and the lever formed integrally because the number of components for the production can be reduced and the assembly work becomes simpler, thereby reducing the production cost even further. The spring member may be firmly attached to the main body by suitable means such as by self-locking nuts or screws. This makes it convenient when the head case is completely removed from the main case, for example, for a maintenance work because the spring member does not become thereby displaced from the main case.
According to still another embodiment of the invention, the head case is made connectable to the main case in a plurality of different connection conditions such that the switch can be operated from different directions and the spring member can be elastically deformed under any of these connecting conditions by contacting a portion of the head case connected to the main case.
The aforementioned forcing member may be a cam, the biasing member being a spring. The cam is held at a non-interfering position so as not to prevent the plunger from being displaced when the head case is connected to the main case and is biased by the biasing spring to cause the plunger to be forcibly displaced against the returning spring when the head case is separated from the main case. In this case, the biasing spring is provided solely for providing a biasing force. Thus, there is a greater degree of freedom in selecting its strength and position, and its desired function can be performed even if the biasing force on the switching mechanism is relatively large.
According to still another embodiment of the invention, the switching mechanism includes fixed terminals, mobile terminals, a mobile member supporting the mobile terminals, a returning spring applying a force on the mobile member so as to bring about the second switched condition where the mobile terminals contact the fixed terminals elastically, the first switched condition being realized by moving the mobile member against the force of the returning spring to separate the mobile terminals away from the fixed terminals. The operating mechanism comprises a plunger which contacts the mobile member, and the forcing means includes a link for applying force directly on the mobile terminals elastically supported by the mobile member so as to forcibly separate the mobile terminals from the fixed terminals. With a switch according to this embodiment, the forcing means does not function if the head case is correctly connected to the main case, and the switching mechanism functions normally. If the head case is separated from the main case, the mobile member is displaced such that the switched condition is changed but the mobile members elastically supported by the mobile member are prevented from being displaced by the forcing means and from contacting the fixed terminals. Thus, although the mobile member is displaced, the switching mechanism is maintained in the first switched condition with the mobile terminals separated from the fixed terminals. Since the plunger is not prevented from being displaced and the link is used to directly prevent the displacement of the mobile terminals elastically supported by the mobile member, only a force large enough to overcome the biasing force for elastically pressing the mobile terminals to the fixed terminals is required in order to forcibly displace the mobile terminals. In other words, the required force is much smaller than that for preventing the plunger from being displaced. Thus, the reaction force from the forcing means to the head case when the head case is connected to the main case is reduced, and the attachment of the head case becomes easier.
The operating mechanism in the head case may preferably be a rotary cam which allows to be operated by a key inserted from outside.
A switch as described above may be conveniently used as a door switch at the entrance to a work area having automatic machine tools installed because even if the head case is removed accidentally from the main case, the switching mechanism is prevented from switching to the second switched condition (or the switched-on condition) while the door is opened.
In another aspect, the invention relates to a switch comprising a switching mechanism which can normally be at a switched-on position in a switched-on condition or at a switched-off position in a switched-off condition, an operating mechanism with a key to be inserted and pulled out to switch the switching mechanism between these conditions and a locking mechanism for normally maintaining the switching mechanism locked in the switched-on condition but releasing it from the locked condition if the key is forcibly pulled out while the key is in the locked condition. Under a normal condition, the locking mechanism functions such that the key cannot be pulled out when the switching mechanism is locked in the switched-on condition but if the key is forcibly pulled out while the key is in the locked condition, the locked condition is mechanically and forcibly released and the switching mechanism is returned to the switched-off condition. The switching mechanism may be structured with fixed terminals, mobile terminals opposite the fixed terminals, a mobile member supporting the mobile terminals and a returning spring, the switching mechanism being in a switched-on condition when the mobile member is displaced by the returning spring to thereby cause the mobile terminals to contact the fixed terminals, the switching mechanism being in a switched-off condition when the mobile member is displaced against the returning spring to thereby separate the mobile terminals from the fixed terminals. The key for the operating mechanism normally causes the switching mechanism to be at the switched-off position in the switched-off condition when it is pulled out and to be displaced against the returning spring to the switched-on position in the switched-on condition when it is inserted. With such a safety feature, damage to the components of the operating mechanism such as a rotary cam and a plunger can be prevented even if the key is pulled out inadvertently or accidentally while the switch is in the locked condition.
According to a preferred embodiment of the invention, such a switch may comprise a plunger formed either integrally with or separately from the mobile member and adapted to be displaced by the operating mechanism and to move the mobile member in coordination therewith, the locking mechanism functioning so as to cause the locked condition by engaging a locking member either with the mobile member or with the plunger, at least a portion of the locking member being more easily breakable than the mobile component engaged with the locking member so as to be damaged and to release the locked condition if a load greater than a specified magnitude is applied thereto. In the above, a portion of the locking member being more easily breakable means that it is either more fragile or weaker than the plunger or the mobile member such that it is easily bent, deformed or broken off. With such a more easily deformable or breakable portion provided, the locking member is damaged at such a predictable portion so as to be released from performing the locking function and a damage to components essential to the switching operation such as the rotary cam operated by the key and the plunger can be reliably avoided. In other words, only the locking member will be required to be replaced.
The locking member of the locking mechanism may be made engageable with the plunger, and the portion of the locking mechanism which engages with the plunger may be caused to bend or deform the locking member or break off when subjected to a load greater than a preset magnitude. Under a normal condition, the locking member thus structured will properly engage with the plunger and prevent the key from being pulled out but if the key is forcibly pulled out while the switch is locked, the locking member is deformed, bent at the position (xe2x80x9cthe engaging partxe2x80x9d) where it engages with the plunger, becoming separated from the plunger such that the locked condition is released and the key becomes removable. Thus, the switching mechanism returns to the switched-off condition in which it should normally be if the key is not inserted. This embodiment can be realized easily and inexpensively because the desired function can be provided merely by changing the shape of a prior art locking member to make is bendable or breakable.
The engaging part of a deformed locking member may be adapted to engage with the mobile member or the plunger at the switched-off position to prevent the mobile member from being displaced to the switched-on position by the biasing force. In this way, if the key is forcibly pulled out while the switch is locked, the engaging part of the bent and deformed locking member at the switched-off position engages with the mobile member or the plunger to keep it at the position. Thus, even if the key is inserted again, the switched-on condition is not brought about, and the damaged condition of the switch is easily ascertained for a repair work.
According to a preferable embodiment, when the engaging part of the mobile member is bent and deformed, it is prevented by contacting the mobile member or the plunger at the switched-on position from moving to the normal locking position. If the key is forcibly pulled out while the switch is locked, the locking member is released from the locked condition, say, by means of an electromagnetic solenoid and, even if the key is inserted again and the switched-on condition is brought about, the locking member with its engaging part bent and deformed cannot advance to the normal locking position. A contact point for monitoring the switching of the locking mechanism to the locking position is connected in series with the switching mechanism such that power cannot be introduced even if the key is inserted again after it is once pulled out forcibly while the switch is locked. In other words, once the key is forcibly pulled out to damage the switch, the locking member becomes unable to advance to its normal locking position. With the use of such a monitoring contact point, inadvertent introduction of power can be prevented.
According to still another embodiment, the locking member locks the switching mechanism in the switched-on position by contacting the mobile member and the contact part at which the locking member contacts the mobile member is made weaker so as to deform or break off by a load greater than a preset magnitude. If the key is forcibly pulled out while the switch is locked, the contacting part of the locking member contacting the mobile member is deformed or breaks off, the locked condition being released and the key being pulled out. Thus, the operating mechanism such as the rotary cam is not damaged and the switching mechanism is set in the normal switched-off condition normally brought about when the key is not inserted. This embodiment can be realized simply and inexpensively by modifying a portion of the locking member contacting the mobile member so as to bend or to break off.
The mobile member may be provided with a groove and the locking mechanism with a holding part which engages in this groove when the mobile member moves to the switched-off position after the contact part is deformed or broken off. In this manner, when the key is forcibly pulled out when the switch is locked, the holding part engages in the groove on the mobile member such that the mobile member which has been displaced to the switch-off position is maintained at this switched-off position and that the switched-on condition is not brought about even if the key is inserted again after it has once been pulled out forcibly. Thus, the damaged condition of the switch is easily ascertained and a repair work can be carried out quickly.
According to still another embodiment, the locking member contacts the mobile member to thereby lock the switching mechanism in the switched-on position, the locking member retracting against the returning spring to allow the mobile member to be displaced to the switched-off position. According to this embodiment, if the key is forcibly pulled out while the switch is locked, the locking member is retracted against the biasing force thereon and hence the locked condition is released. The rotary cam and the plunger are not damaged and the switching mechanism returns to the switched-off condition as it normally should when the key is not inserted. This desired function is achievable inexpensively, say, by merely forming a cam surface at the contacting part such that the locking member will be retracted when an excessively large load is applied.
The displaced mobile member may be further so arranged to become engaged to and held by the locking member when a load greater than a preset magnitude is applied. With this arrangement, if the key is forcibly pulled out while the switch is locked, not only is the locking member retracted against the biasing force thereon and the switching mechanism returns to the switched-off condition, but the mobile member retracted to the switched-off position is engaged to and held by the mobile member which has been retracted so as not to move to the switched-on position even if the key is inserted again. Thus, the damaged condition of the switch can be easily ascertained and a repair work can be quickly carried out.
According to a preferred embodiment, there are a plurality of plungers or mobile members. The locking mechanism locks the switching mechanism by engaging the locking member with one of the mobile members or plungers. The engaged one of the mobile members or plungers is deformed so as to unlock the switching mechanism when a load greater than a specified magnitude is applied to the key while the switching mechanism is locked. Such plungers may be formed either integrally with the mobile member or separately. With a switch thus formed, the mobile member or the plunger to which the locking member is engaged is damaged if the key is forcibly pulled out while the switching mechanism is locked. The locked condition is released and the key is pulled out. Thus, neither the rotary cam nor the plunger will be damaged and the switching mechanism is set in the normal switched-off condition.
According to still another embodiment of the invention, an electromagnetic solenoid is provided for locking and unlocking the switching mechanism and the terminals undergo switching operations accordingly as the switching mechanism is locked and unlocked. Such a switch can be conveniently used as a door switch at the entrance to a work area with machine tools for switching power on and off for these machine tools.